Electric work machine

ABSTRACT

An electric work machine, such as a lawn mower includes a motor case (22) fixed inside a main-body housing (10). A brushless motor (21) is housed inside the motor case (22) and includes a stator (23) having a stator core (40), coils (45), and upper and lower insulators (42, 43), and a rotor (24) disposed inward of the stator (23) and having a rotary shaft (25). A spindle (17) is driven by the rotary shaft (25). The motor case (22) holds the stator (23) and axially supports the rotary shaft (25) via bearings (68, 76). One or more insulating members, such as an insulating cap (67) and/or a resin layer (78), provide electrical insulation between the stator core (40) and the rotary shaft (25).

CROSS-REFERENCE

The present application claims priority to Japanese patent applicationserial number 2018-190305 filed on Oct. 5, 2018, the contents of whichare incorporated fully herein by reference.

TECHNICAL FIELD

The present invention generally relates to electric work machines, suchas power tools, gardening tools (e.g., lawn mowers and other types ofoutdoor power equipment), air compressors for pneumatic tools, and thelike. In some embodiments, the present invention concerns improvedelectrical insulation features provided between a rotary shaft andstator core of a brushless motor and/or between the rotary shaft and arotor core that holds and rotatable drives the rotary shaft.

BACKGROUND ART

In some electric work machines (e.g., power tools), a brushless motor,which is compact and highly durable, is used as a power source. Forexample, Japanese Laid-open Patent Publication 2017-7068 discloses aninner-rotor-type brushless motor that comprises a tubular-shaped statorand a rotor, which is disposed in the interior of the stator. Inaddition, in the brushless motor, coils are wound on a stator corethrough insulators that are made of resin, thereby providing electricalinsulation between the stator core, which has a metal interior, and thecoils, which are energized during operation.

SUMMARY OF THE INVENTION

However, if the brushless motor is to be housed in an interior case madeof metal, a problem may result if there is insufficient electricalinsulation between the stator core and a rotary shaft driven by therotor.

Accordingly, one non-limiting object of the present teachings is toprovide an electric work machine that can provide effective insulationbetween a stator core and a rotary shaft.

Additional objects of the present teachings will become apparent uponreading the following description of embodiments of the presentteachings.

In a first aspect of the present teachings, an electric work machinepreferably comprises an interior case fixed inside an exterior housing.A brushless motor is housed inside the interior case and comprises: astator having a stator core, one or more coils, and an insulatorinterposed between the stator core and the coil(s); and a rotor disposedinward of the stator and having a rotary shaft, which drives an outputpart. The interior case holds the stator and axially supports the rotaryshaft via a bearing. An insulating means provides electrical insulationbetween the stator core and the rotary shaft.

In a second aspect of the present teachings, another insulating memberis provided on the rotary-shaft side and is interposed between a rotorcore, which is provided in the rotor, and the rotary shaft.

In a third aspect of the present teachings, the insulating meansincludes a bearing-side insulating member that is provided in or on aportion of the interior case that axially supports the rotary shaft viathe bearing.

In a fourth aspect of the present teachings, the bearing-side insulatingmember is integrally formed on the interior case.

In a fifth aspect of the present teachings, the insulating meansincludes a stator-side insulating member that is provided (disposed)between the interior case and the stator core.

In a sixth aspect of the present teachings, the stator-side insulatingmember is integrally formed on (joined to) the interior case.

In a seventh aspect of the present teachings, an electric work machinepreferably comprises a brushless motor comprising a stator having astator core, one or more coils, and an insulator interposed between thestator core and the coil(s), and a rotor disposed inward of the statorand having a rotary shaft, which drives an output part. A stator-supportmember supports the stator and a housing supports the stator-supportmember. An insulating means provides electrical insulation between thestator core and the rotary shaft.

In an eighth aspect of the present teachings, another insulating memberis interposed between the housing and the stator core.

Effects of the Invention

One non-limiting effect of the present teachings is that, by using aninsulating means according to the present teachings, effectiveinsulation can be provided, e.g., between the stator core and the rotaryshaft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a center, longitudinal, cross-sectional view of a lawn moweraccording to one embodiment of the present teachings.

FIG. 2 is an enlarged view of a motor unit of the lawn motor.

FIG. 3 is an oblique view of the motor unit.

FIG. 4 is an exploded oblique view of the motor unit.

FIG. 5 is a longitudinal, cross-sectional view of the motor unit.

FIG. 6 is a transverse, cross-sectional view of an upper-case portion ofthe motor unit.

FIG. 7 is transverse, cross-sectional view of a lower-case portion ofthe motor unit.

FIG. 8 is an explanatory diagram of a steel plate of a stator core andsplit molds.

FIG. 9 is an oblique view of a brushless motor according to the presentteachings.

FIG. 10 is a plan view of a stator of the brushless motor.

FIG. 11 is a bottom view of the stator.

FIG. 12 is an oblique view of a short-circuiting member (first to thirdmetal fittings alone are indicated by solid lines).

FIG. 13 is another oblique view of the short-circuiting member (first tothird metal fittings alone are indicated by solid lines).

FIG. 14 is an exploded oblique view of the short-circuiting member.

FIG. 15 is a diagram for explaining a coil winding method.

FIG. 16 is an explanatory diagram in which a wiring state created by thefirst to third metal fittings is viewed from the plane of the stator.

FIG. 17 is a wiring circuit diagram of the first to third metalfittings.

FIG. 18 is an explanatory diagram of a modified example of a relativerotation impeding part of the stator.

FIGS. 19A-E are explanatory diagrams of modified examples of arotation-impeding part and a slippage-impeding part of a rotary shaft.

FIG. 20 is an explanatory diagram that shows a double-insulatedstructure of a compressor.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of the present teachings are explained below, with referenceto the drawings.

Explanation of a Representative Lawn Mower

FIG. 1 is a center, longitudinal, cross-sectional view that shows arechargeable lawn mower 1, which is one example of an electric workmachine according to the present teachings, and FIG. 2 is an enlargedview of a motor unit portion thereof.

The lawn mower 1 comprises: a base (deck) 2, which extends in arear-front direction and has an open lower surface; a main body 3, whichis coupled to a center upper side of the base 2; and a handle 4, whichextends from the base 2 rearward and diagonally upward.

The base 2 has two pairs of wheels 5, 5, one pair forward and one pairrearward, and can be moved forward and rearward by using the handle 4.Downward of the handle 4, a rear cover 6 and a grass-collection basket(grass catcher) 7 are provided on a rear portion of the base 2. A switchlever 8 is provided on a rear end of the handle 4; and forward thereof,a lock-OFF button 9 is provided that, in a normal state, locks theoperation of the switch lever 8. Pressing the lock-OFF button 9 unlocksthe switch lever 8, so that it becomes possible to pull the switch lever8.

The main body 3 comprises a main-body housing (cowling) 10, which has alower end tubular part 11 that opens downward and protrudes into thebase 2. A battery-mount part 12, into which one or more battery packs 13that serve as a power supply for the lawn mower 1 can be inserted from arear upper side, is formed on an upper part of the main-body housing 10in an inclined manner such that it is lower in the front. Thebattery-mount part 12 is openable and closable by a battery cover 14.

In addition, on a front part of the main-body housing 10, a controller15 comprising a control circuit board (not shown) is supported such thatit extends vertically in an up-down direction. Rearward thereof, a motorunit 16 is provided downward of the battery-mount part 12. A rotaryshaft 25 of a brushless motor 21, which is described below, protrudesdownward from the motor unit 16, and a spindle 17 is coaxially coupledto a lower end of the rotary shaft 25. The spindle 17 protrudes downwardfrom the tubular part 11 into the base 2, and a horizontal, plate-shapedcutting blade 20 is orthogonally attached to a lower end of the spindle17 by using an inner flange 18 and a bolt 19. The spindle 17 is onenon-limiting example of an output part according to the presentteachings.

As shown in FIGS. 2-4, the motor unit 16 comprises the brushless motor21 and a motor case 22, which holds the brushless motor 21. Thebrushless motor 21 is an inner-rotor type that comprises atubular-shaped stator 23 and a rotor 24, which passes through theinterior of the stator 23 and has the rotary shaft 25 at its axialcenter. The motor case 22 comprises an upper case 26 and a lower case27, which hold the stator 23 from above and below and axially supportthe rotary shaft 25. The lower case 27 of the motor case 22 is joined toa mounting base 28, which is provided on an upper side of the tubularpart 11. A motor cover 29, which covers the motor unit 16 from above, isprovided upward of the mounting base 28. The upper case 26 and lowercase 27 are typically made of metal.

On the other side of the motor unit 16, a bearing retainer 30, whichaxially supports the spindle 17 via a bearing 31, is joined, from belowby a plurality of screws 32, to a lower side of the mounting base 28. Alower end of the spindle 17 passes through the bearing retainer 30 andalso passes through a baffle plate 33, which is screwed onto a lower endof the tubular part 11, so as to protrude into the interior (grasscutting) space defined by the base 2. A tube part 34 mates with thelower end of the spindle 17, and is provided on the inner flange 18, onwhich the cutting blade 20 is mounted. A centrifugal fan 35 is providedon the outer circumference of the tube part 34.

Explanation of a Representative Stator

As shown in FIGS. 4-7, the stator 23 of the brushless motor 21 comprisesa stator core 40 composed of a plurality of steel plates 40 a laminated(stacked) in an axial direction (FIG. 8), and a plurality of (here,twelve) teeth 41 protrude inwardly. An upper insulator 42 and a lowerinsulator 43, which are made of resin or polymer, serve as electricallyinsulating members, and are integrally formed on both the upper andlower ends of the stator core 40. An insulation part 44, which is alsomade of resin or polymer, is continuous with and integrally formed withthe upper and lower insulators 42, 43, i.e. insulating parts 42-44 aremade from the same integral piece of resin or polymer. The insulationpart 44 covers an inner-circumferential surface of the stator core 40and an outer-circumferential surface of the teeth 41, except for theprotruding end surfaces of the teeth 41. Coils 45 are respectively woundaround each tooth 41 through (adjacent) the insulation part 44. Ashort-circuiting member 46, which is electrically connected to the wiresthat form the coils 45 and that forms (defines) a three-phaseconnection, and a sensor circuit board 47, which detects the rotationalposition of the rotor 24, are joined (attached) to the upper insulator42. Further details concerning the upper and lower insulators 42, 43,the short-circuiting member 46, and the sensor circuit board 47 areprovided below.

Three ridges 48A, 48A, 48B are formed on a circumferential surface ofthe stator core 40 such that they are equispaced in the circumferentialdirection. Among these, the ridges 48A, 48A each have a taperedtransverse-cross-sectional shape in which the width in thecircumferential direction becomes small toward the outer side of thestator core 40 in the radial direction. On the other hand, the ridge 48Bis not tapered, but rather has a quadrilateral,transverse-cross-sectional shape in which its width in thecircumferential direction does not vary along the radial direction.Slight rounds (curved surfaces), which expand outward along thecircumferential direction, are provided on radially outward end surfacesof the ridge 48B. In addition, a through hole 49 is formed in each ofthe ridges 48A, 48B.

The ridges 48A, 48B are formed such that they overlap projections 50A,50B formed on each of the steel plates 40 a as shown in FIG. 8. Amongthese, the projections 50A are each formed with a taper in which thewidth in the circumferential direction becomes small toward the outerside of the stator core 40 in the radial direction. On the other hand,the projection 50B is not tapered but rather has a quadrilateral shapein which the width in the circumferential direction does not vary alongthe radial direction. Pass-through holes 51 are formed in each of theprojections 50A, 50B. Slight rounds (curved surfaces), which expandoutward along the circumferential direction, are provided on radiallyoutward end edges of the projection 50B. In addition, a notch 52 isformed between each adjacent pair of the projections 50A, 50B, and agrooves 53 (FIG. 7) for positioning during manufacture of the stator isformed between each adjacent pair of the ridges 48A, 48B.

The ridges 48A are tapered in this way to avoid interference with a moldat the time that the upper and lower insulators 42, 43 and theinsulation part 44 are integrally formed by insert molding. That is, asshown by a chain double-dashed line in FIG. 8, when the upper and lowerinsulators 42, 43 and the insulation part 44 are to be integrally formedon (joined to) the stator core 40 by using left and right split molds54, 54, the two tapered ridges 48A, 48A are positioned, one on the leftand one on the right, with respect to the split molds 54, 54, and theridges 48A, 48A are set such that they do not interfere, owing to theirtapered surfaces, with the split molds 54, 54, which move in the leftand right directions in FIG. 8. In the present embodiment, although theangle θ of the taper with respect to the movement direction is set to3°, but the angle θ of the taper with respect to the movement directionmay be set, e.g., within a range of 1°-10°. In addition, because roundsthat expand (widen) outward also are provided on the end surfaces of theridge 48B, interference with the left and right split molds 54, 54 isprevented.

Referring now to FIGS. 2 and 5-7, the rotary shaft 25 of the rotor 24passes through the axial center of a circular-cylindrical-shaped rotorcore 55, which is composed of a lamination of a plurality of steelplates in the axial direction. The rotor core 55 and the rotary shaft 25are integrally joined (connected, held) together by a resin 56. A bevelpart 57 (FIG. 4) is formed on the lower end of the rotary shaft 25.

The resin 56 may also be referred to as a resin insert, a resin sleeve,a resin bushing, a polymer insert, a polymer sleeve, a polymer bushing,etc., or any variations or combinations thereof. The resin 56 is thusnot limited to naturally occurring resins and may comprise naturaland/or synthetic polymers. Furthermore, the basic requirement of theresin 56 is that it is interposed between the rotor core 55 and rotaryshaft 25, which are both typically made of a metal, and serves toconnect or hold them together, so that the rotor shaft 25 rotatesintegrally with the rotor core 55, i.e. they are rotationally-fixed. Theresin 56 also is preferably design to prevent slippage of the rotaryshaft 25 relative to the rotor core 55 in or along the axial directionof the rotary shaft 25.

The resin or polymer that constitutes the resin 56 optionally may bereinforced with fibers, e.g., glass fibers, carbon fibers, etc., andpreferably exhibits electrical insulation properties. For example, theresin 56 preferably has a resistivity of 1×10¹⁰ Ω·m or higher, morepreferably 1×10¹² Ω·m or higher, and/or a conductivity of 1×10¹⁰ σ orless, more preferably 1×10¹² σ or less.

As shown in FIG. 5, a diamond knurl 25 a or other type of knurling orgripping pattern may be formed on the outer circumference of the rotaryshaft 25 along all or only a portion of the length of the rotary shaft25 that contacts the resin 56. The knurl 25 a provides an unevenness orroughness that is formed, e.g., in a lattice or grid shape on theouter-circumferential surface of the rotary shaft 25. The knurl 25 aacts as a rotation-impeding part and/or a slippage-impeding part,because the knurl 25 a enables the resin 56 to securely grip the rotaryshaft 25, so that no rotation of the rotary shaft 25 relative to theresin 56 is possible and/or so that no axial slippage/movement of therotary shaft 25 relative to the resin 56 is possible. The knurl 25 ashown in FIG. 5 is merely one example of an uneven surface that canperform one or both of the rotation-impeding function and/or the axialslippage-impeding function, and additional examples will be providedbelow.

In addition, multiple (here, eight) magnet holes 58 are concentricallyformed in a circumferential-edge part of the rotor core 55 such thatthey pass through in the axial direction thereof. Plate-shaped permanentmagnets 59 are embedded (inserted) in the magnet holes 58. By formingthrough holes in the steel plates 40 a, except at the upper and lowerends, that are aligned in the axial direction, spaces (cutouts, voids)60 are formed radially inward of the permanent magnets 59, which reducesthe weight of the rotor 24.

Explanation of a Representative Motor Case

The upper case 26 and the lower case 27 of the motor case 22 are eachcircular-cup-shaped and cover an upper part and a lower part,respectively, of the stator 23.

The upper case 26 is formed of a nonmagnetic material, e.g., a metalsuch as an aluminum alloy. As shown in FIGS. 3-5, fins 65 fordissipating heat are provided, from the upper surface of the outercircumference down along the side surface of the upper case 26 andextending in the up-down direction, at prescribed spacings in thecircumferential direction. In addition, an upper-bearing retaining part66 is formed at the center of the upper surface of the upper case 26. Abearing 68 is held in the upper-bearing retaining part 66 by aninsulating cap 67, which is made of resin or polymer, and rotatablysupports an upper end of the rotary shaft 25. A pass-through hole 69 isformed at the center of the upper-bearing retaining part 66 and isclosed up by a resin or polymer cap 70.

The resin or polymer of the insulating cap 67 and the resin cap 70 maybe selected from any of the resins described above with regard to resin56, which description is equally applicable to the insulating cap 67 andresin cap 70.

Furthermore, three screw-boss parts 71A, 71A, 71B, which projectradially outward, are formed on the circumferential surface of the uppercase 26 such that they extend in the up-down direction and areequispaced in the circumferential direction. The screw-boss parts 71A,71B correspond to the ridges 48A, 48B of the stator core 40. Inparticular, the lower ends of the screw-boss parts 71A, 71B are open andhave either a tapered shape in transverse cross section or aquadrilateral shape in transverse cross section that mates with therespective ridges 48A, 48B. A slit 72, which extends upward from a lowerend of the upper case 26, is formed in or on the circumferential surfaceof the upper case 26 between the ridges 48A, 48B.

Turning now to the lower case 27, it comprises a circular-shaped endsurface part 73, in which a lower-bearing retaining part 74 is formed atthe center, the same as in the upper case 26. A tubular part 75 risesupward from the outer circumference of the end surface part 73. Abearing 76 is held by the lower-bearing retaining part 74 and supportsthe rotary shaft 25, which passes through the lower-bearing retainingpart 74. Bosses 77 for fastening screws to the mounting base 28 areformed on the outer circumference of the tubular part 75 so as to pointdownward at four locations equispaced in the circumferential direction.

In addition, a resin layer 78 is formed on (joined to) an inner surfaceof the end surface part 73 (except for the lower-bearing retaining part74), an inner circumference of the tubular part 75, and an outercircumference of the tubular part 75 (except for on the bosses 77), suchthat the resin layer 78 continuously covers from the inner surface ofthe end surface part 73 to the inner circumference and then to the outercircumference of the tubular part 75. Boss parts 79A, 79B have shapesthe same as the corresponding screw-boss parts 71A, 71B of the uppercase 26, and are formed, extending in the axial direction, at locationsof the resin layer 78 corresponding to the ridges 48A, 48B of the statorcore 40. Through holes, which have tapered shapes in transverse crosssection or quadrilateral shapes in transverse cross section and matewith the respective ridges 48A, 48B, are formed in the upper ends of theboss parts 79A, 79B. Furthermore, recessed grooves 80 are formedcontinuously on the lower sides of the boss parts 79A, 79B.

Again, the resin of the resin layer 78 may be selected from any of theresins or polymers described above with regard to resin 56, whichdescription is equally applicable to the resin layer 78.

Thus, the upper case 26 of the motor case 22 is placed onto the upperportion the stator 23 by aligning the ridges 48A, 48B of the stator core40 with the respective screw-boss parts 71A, 71B of the upper case 26and then inserting the ridges 48A, 48B into the corresponding screw-bossparts 71A, 71B. The upper bearing 68, which is joined to the upper endof the rotary shaft 25 of the rotor 24, is held by the upper-bearingretaining part 66. On the other side, the lower case 27 placed on thelower portion of the stator 23 by aligning the ridges 48A, 48B of thestator core 40 with the boss parts 79A, 79B of the lower case 27 andthen inserting the ridges 48A, 48B into the corresponding boss parts 79,79B. The lower bearing 76, which is joined to the lower end of therotary shaft 25, is held by the lower-bearing retaining part 74. In thisassembled state, screws 81 are inserted, from below, into the boss parts79A, 79B of the lower cases 27, then passed through the ridges 48A, 48B,and are screwed into the screw-boss parts 71A, 71B of the upper case 26.As a result, the brushless motor 21 is covered by the upper case 26 andthe lower case 27, except for an intermediate portion of the outercircumference of the stator core 40, and thereby the motor unit 16 isobtained.

In this state, the brushless motor 21 contains a basic-insulation member(the upper and lower insulators 42, 43 and the insulation part 44, whichare integrally formed), which is interposed between the stator core 40,which has a metal interior, and the coils 45, which are energized(supplied with current) during operation of the brushless motor 21.

In addition thereto, supplementary electrical insulation is provided by:(i) the resin 56, which serves as an insulating member on therotary-shaft side and is interposed between the rotary shaft 25 and therotor core 55, (ii) the insulating cap 67, which is interposed betweenthe upper case 26 and the rotary shaft 25, and (iii) the resin layer 78,which is interposed between the tubular part 75 of the lower case 27 andthe stator core 40. Therefore, the space between the stator core 40 andthe rotary shaft 25 is double insulated. In addition, by providing anadjustable gap in the up-down direction between the upper case 26 andthe lower case 27, assembly of the motor unit 16 is not negativelyinfluenced even if the dimension (length) of the stator 23 in the axialdirection changes.

When the motor unit 16 is placed, with the rotary shaft 25 facingdownward, on the mounting base 28 and screws are screwed into the bosses77 from below the mounting base 28, the motor unit 16 is fixed to themounting base 28. Concentric arcuate ribs 73 a (FIGS. 2, 5), which matewith the tubular part 11 to position the motor unit 16, are formed onthe lower surface of the end surface part 73 of the lower case 27.

In the present embodiment, when the motor cover 29 is put on, the motorunit 16 is mostly covered while a center portion of the upper case 26that includes the upper-bearing retaining part 66 is exposed. In thisstate, the fins 65 of the upper case 26 are proximate to the innersurface of the motor cover 29.

Furthermore, the stator 23 of the brushless motor 21 is impeded(blocked) from rotating relative to the motor case 22 by the screws 81,which pass through the ridges 48A, 48B, and also by the screw-boss parts71A, 71B of the upper case 26 and the boss parts 79A, 79B of the lowercase 27, which respectively mate with (engage) the ridges 48A, 48B.

Explanation of Representative Upper and Lower Insulators

Referring now to FIGS. 9 and 10, the upper insulator 42 is a ring bodythat is integrally formed on (joined to) an upper-side end surface ofthe stator core 40. Twelve terminal-holding parts 85, which respectivelyhold fusing terminals 99 provided on the short-circuiting member 46, areprovided on an upper surface of the upper insulator 42 equispaced in thecircumferential direction. In each of the terminal-holding parts 85, aninner-wall part 86 on the inner-circumference side and an outer-wallpart 87 on the outer-circumference side extend vertically and are spacedapart radially by a spacing (distance) that substantially corresponds tothe diameter of wires 115. A mating groove 88, which mates with itscorresponding fusing terminal 99, is formed between the inner-wall part86 and the outer-wall part 87 at the center in the circumferentialdirection. In addition, stop bosses 89 for joining to (attaching) theshort-circuiting member 46 protrude from the upper surface of the upperinsulator 42 at five locations, i.e., at locations at which they contactthe base of every other tooth 41.

As shown in FIG. 11, the lower insulator 43 is a ring body that isintegrally formed on (joined to) the lower-side end surface of thestator core 40. Twelve vertically-extending guide walls 90 are providedalong the circumferential direction on the lower surface of the lowerinsulator 43 at locations slightly shifted in the circumferentialdirection from the bases of the teeth 41.

Explanation of a Representative Short-Circuiting Member and SensorCircuit Board

Still referring to FIGS. 9-10, the short-circuiting member 46 includes aring body made of resin, polymer, etc. and has a circumference that issmaller than the circumference of the upper insulator 42. Five matingbosses 95, which are quadrilateral-tube-shaped and respectively mate,from above, with the stop bosses 89 of the upper insulator 42, and threeribs 96, which respectively engage with the grooves 53 of the statorcore 40, protrude from the outer circumference of the short-circuitingmember 46.

In addition, the short-circuiting member 46 is formed in steps such thatits thickness in the axial direction becomes smaller in steps, startingfrom the upper surface, from the outer circumference toward the innercircumference. Furthermore, as shown in FIGS. 12-14, a first metalfitting 97U having the maximum diameter and that is located in anouter-circumferential portion having the greatest wall thickness, asecond metal fitting 97W having an intermediate diameter and that islocated in an intermediate-wall-thickness portion on the inner sidethereof, and a third metal fitting 97V having the minimum diameter andthat is located in an inner-circumference portion on the inner sidethereof are concentrically disposed in the thickness portions and insertmolded. The letters U, W, and V appended to the metal fittings indicatedthe corresponding phases of the three-phase current: U phase, W phase,and V phase.

Each of the first to third metal fittings 97U-97V is a strip-shaped,curved plate having a substantially C shape in plan view. Protrudingpieces 98 protrude radially outward at four locations, namely, at bothends and at locations point symmetric with the two ends of the metalfittings 97U-97V. One of the fusing terminals 99 is formed at the tip ofeach protruding piece 98 by first bending it downward, then folding itupward, and further bending it outward. A welding part 101 for spotwelding a power-supply line 100U is formed at the base of the protrudingpiece 98 on (at) one end of the first metal fitting 97U. In addition,welding parts 101 for spot welding power-supply lines 100W, 100V areformed on (at) the bases of the protruding pieces 98 of the second andthird metal fittings 97W, 97V on (at) the ends on the side opposite thatof the first metal fitting 97U.

In the state in which the first to third metal fittings 97U-97V aredisposed and insert-molded inside the resin ring body of theshort-circuiting member 46, starting from above, in the order of thefirst metal fitting 97U, the second metal fitting 97W, and the thirdmetal fitting 97V, such that their phases are shifted by a prescribedangle in the circumferential direction, the fusing terminals 99respectively protrude from the outer-circumferential surface of theshort-circuiting member 46 without contacting each other and aresubstantially equispaced in the circumferential direction. Pass-throughholes 102, which respectively expose the welding parts 101 of the metalfittings 97U-97V, are formed in the short-circuiting member 46 such thatthe pass-through holes 102 are offset by prescribed spacings in oneportion in the circumferential direction. The power-supply lines100U-100V are respectively spot welded to the welding parts 101. A notch103 for drawing the power-supply lines 100U-100V to the outer side isformed between two of the welding parts 101 such that only the lowerside of the short-circuiting member 46 is connected to (via) the notch103.

In addition, support pieces 104, which comprise mount bosses 105 formounting the sensor circuit board 47, radially inwardly protrude fromthe inner circumference of the short-circuiting member 46 atpoint-symmetric positions. Support pieces 106 (FIG. 13), which supportthe outer circumference of the sensor circuit board 47, radiallyinwardly protrude from the inner circumference of the short-circuitingmember 46 between the support pieces 104.

As shown in FIG. 10, the sensor circuit board 47 has an arcuate stripshape that extends around the inner side of the short-circuiting member46. Mating holes 107, which respectively mate with the mount bosses 105of the support pieces 104, are formed on both circumferential ends ofthe sensor circuit board 47. Because the mount bosses 105 mate with themating holes 107 and the outer circumference of the sensor circuit board47 is supported by the support pieces 106, the sensor circuit board 47is held on the inner-circumference side of the short-circuiting member46. Rotation-detection devices 108 (FIG. 11), such as Hall-effectdevices, which detect the magnetic fields of the permanent magnets 59provided on the rotor 24, are installed on a back surface of the sensorcircuit board 47. Signal lines 109, which are connected to the sensorcircuit board 47, and the power-supply lines 100U-100V are drawn throughthe notch 103 of the short-circuiting member 46 to the outer side. Thisdrawn-out position corresponds to the slit 72 provided in the upper case26 of the motor case 22.

When the five mating bosses 95 on the outer circumference are mated withthe stop bosses 89, which are provided on the upper surface of the upperinsulator 42, and are screwed to the stop bosses 89 from above usingscrews 91 (FIG. 10), and when the tips of the three ribs 96 are engagedwith the grooves 53 of the stator core 40, and the fusing terminals 99are caused to be held by the terminal-holding parts 85 of the upperinsulator 42, the short-circuiting member 46 is joined, together withthe sensor circuit board 47, to the stator 23. In particular, becausethe ribs 96 engage with and hold fast to the grooves 53 at threelocations, the ribs 96 function as anchors that stably support theshort-circuiting member 46. The power-supply lines 100U-100V and thesignal lines 109 are drawn out from the slit 72, which is provided inthe upper case 26, to the exterior through a sleeve-shaped gasket 82(FIG. 3), which is fitted into the slit 72.

Explanation of a Representative Coil-Forming Method

Twelve of the coils 45 herein are formed at the same time, using threewinding nozzles, by starting windings, using a single wire 115 as shownin FIG. 15 (however, when distinguishing wires, the symbols A-C areappended, as in 115A, 115B, 115C, and the same applies to other portionshereinbelow) on three of the teeth 41 located at 120° spacings, andwinding, in order, the four teeth 41 adjacent in the circumferentialdirection of the stator 23. For example, with regard to the wire 115Ashown in FIG. 15, after a start end 116A has been initially latched(attached) to the corresponding fusing terminal 99, the coils 45 areformed, in order, on the teeth 41 adjacent in the clockwise direction.The winding direction at this time is the counterclockwise direction,facing the teeth 41. In addition, a crossover wire 117A after formingeach coil 45 returns to the upper insulator 42 side (wiring-connectionside) and latches (attaches) to the fusing terminal 99 between two ofthe teeth 41, 41.

Furthermore, after the fourth coil 45 has been formed, as shown in FIG.11, the wire 115A is first drawn out to the lower insulator 43 side(opposite wiring-connection side) and wound from the outer side of theguide wall 90 at the base of the tooth 41 being wound, after which thewire 115A once again returns to the upper insulator 42 side, is latched(attached) to the fusing terminal 99 to which a start end 116B of theseparate adjacent wire 115B is latched, and becomes a terminal end 118A,as shown in FIG. 15. Thereupon, the orientation of the start end 116B ofthe separate wire 115B and the orientation of the terminal end 118A aremade to coincide and can be simultaneously cut at the portion at whichthey are completely surrounded. This applies likewise for a terminal end118B of the wire 115B and the start end 116A of the wire 115C, as wellas a terminal end 118C of the wire 115C and the start end 116A of thewire 115A.

The first to third metal fittings 97U-97V of the short-circuiting member46 are disposed such that their phases are shifted in thecircumferential direction one coil 45 at a time. As shown in FIG. 16,crossover wires 117A-C, which are disposed between the twelve coils 45,are each fused with respect to three adjacent coils 45. In FIG. 16, tomake it easy to distinguish the crossover wires 117A-C to which themetal fittings 97U-97V are fused, linear hatching is applied to thefirst metal fitting 97U, cross hatching is applied to the second metalfitting 97W, and dots are applied to the third metal fitting 97V.

Thus, the three coils 45 adjacent in the circumferential direction areconfigured as a delta connection of U (W-U), V (U-V), W (V-W) phases bythe first to third metal fittings 97U-97V of the three phases. This isbecause four sets are sequentially arranged in parallel by the first tothird metal fittings 97U-97V; and the three-phase circuit herein isformed as shown in FIG. 17. This is equivalent to a delta connection inwhich the four coils U1-U4, V1-V4, W1-W4 of each of the U, V, and Wphases are connected in parallel.

Operation of the Representative Lawn Mower

In the lawn mower 1 configured as described above, when the switch lever8 is unlocked by pressing the lock-OFF button 9 and the switch lever 8is pulled, a main switch turns ON and an ON signal is transmitted fromthe battery pack 13 to the control circuit board of the controller 15. Amicrocontroller of the control circuit board acquires the rotationalstate of the rotor 24 based on detection signals obtained from therotation-detection devices 108 of the sensor circuit board 47, turnsON/OFF switching devices, which are provided on the control circuitboard, in accordance with the acquired rotational state, and supplieselectric current, in order, to the coils 45, for each phase, of thestator 23, and thereby rotates the rotor 24. Thus, when the rotary shaft25 rotates and causes the spindle 17 to rotate together with the cuttingblade 20, and when the base 2 is pushed using the handle 4, it becomespossible to cut grass with the cutting blade 20 while the lawn mower 1travels via the wheels 5.

At this time, the stator 23 of the brushless motor 21 is impeded(blocked) from rotating relative to the motor case 22, which is joinedto the mounting base 28, by the screws 81 that pass through the ridges48A, 48B. Therefore, any effects caused by manufacturing tolerances aresmall and it becomes possible to impede (block) relative rotation of thebrushless motor 21 and the motor case 22 with good accuracy. Inaddition, high strength is also obtained. In particular, because thescrews 81 pass directly through the stator core 40, flexure tends not tooccur on the outer side of the stator core 40, as compared with astructure that couples upper and lower cases of a motor case usingscrews that do not pass through the stator core.

Furthermore, because the wires 115 that form the coils 45 do not crossone another, scraping of the wires 115 caused by contacting each othertends not to occur, and therefore durability is also increased.

Furthermore, in the rotor 24, because the diamond knurl 25 a is providedon the outer circumference of the rotary shaft 25, the bite or grip ofthe resin 56 is increased, thereby reducing or minimizing slippage inthe rotational direction and the axial direction. Consequently, theintegration (secure attachment) of the rotary shaft 25 and the rotorcore 55 is maintained even if the load on the rotary shaft 25 producedby the rotation of the cutting blade 20 becomes large.

Advantages of the Representative Stator Core

In the lawn mower 1 of the above-mentioned embodiment, screw members(the screws 81) pass through the stator core 40 of the brushless motor21 and furthermore, the through holes 49 are formed to impede (block)the relative rotation of the stator 23. Therefore, it is possible toimpede (block) relative rotation of the stator 23 using the stator core40, which has high accuracy and high strength, instead of by using theupper and lower insulators 42, 43 to impede (block) relative rotation.Thereby, the stator 23 can be impeded (blocked) from rotating relativeto the motor case 22 with high accuracy and high strength.

In addition, because cover members (the upper case 26 and the lower case27) are provided on both ends of the stator 23 in the axial direction inthe present embodiment, and because the rotation-impeding parts (theridges 48A, 48B), which mate with the upper case 26 and the lower case27, are provided on the outer circumference of the stator core 40,rotation of the stator 23 relative to the motor case 22 can be impeded(blocked), using the stator core 40, with high accuracy and highstrength.

Furthermore, because protruding parts (the ridges 48A, 48B) for impedingrelative rotation by engaging with the cover members (the upper case 26and the lower case 27) are formed on the outer circumference of thestator core 40, and because the through holes 49, which are provided forthe screws 81 to pass through, are formed in the ridges 48A, 48B,rotation of the stator 23 relative to the motor case 22 can be impeded(blocked), using the ridges 48A, 48B and the screws 81, with highaccuracy and high strength.

Furthermore, because the ridges 48A, 48A have a tapered shape intransverse cross-section such that the width in the circumferentialdirection gradually narrows toward the outer side in the radialdirection of the stator core 40, interference with the split molds 54can be prevented when the upper and lower insulators 42, 43 and theinsulation part 44 are being integrally formed.

It is noted that, in the stator core, the number, shape, or the like ofthe ridges that impede (block) relative rotation of the stator is notlimited to the above-mentioned embodiment. For example, the number ofridges can be increased or decreased, the transverse-cross-sectionalshape can be modified where appropriate, or the like. In anothermodified example, the ridges do not necessarily have to be providedacross the entire up-down length of the stator core and may instead beprovided across a distance shorter than the overall length, such as anupper-end side, a lower-end side, an intermediate region, or the like.Relative rotation can also be impeded (blocked) by passing the screwmembers through the stator core, without providing the ridges.

In addition, the rotation-impeding function is not limited to beingeffected by the ridges, the through holes, and the like. For example, asshown in FIG. 18, axially-extending recesses 61 may be formed on (in)the outer-circumferential surface of the stator core 40 and the screws81 may be mated (engaged) in the recesses 61 in order to impede rotationof the stator 23 relative to the motor case 22. In this modifiedembodiment too, the stator 23 can be impeded (block) from rotating usingthe stator core 40, which has high accuracy and high strength.

Furthermore, the rotation-impeding function can also be effected byusing the through holes and the recesses in combination. The screwmembers may be bolts. The target of the rotation impeding is also notlimited to the motor case; that is, if there is no motor case, thenrotation of the stator relative to the motor housing or the like may beeffected using the through holes, the recesses, or the like.

It should be noted that, although an electric work machine, in which amotor is fixed to a housing via a motor case was explained, the presentteachings can also be applied to electric work machines in which a motoris fixed directly to the housing by fastening screws through throughholes provided in the stator core. In such embodiments as well, theridges may be mated with the housing.

In addition, if rotation is impeded (blocked) by mating the ridges withthe housing, it is also possible to fix the brushless motor bysandwiching the brushless motor between the half housings. In such anembodiment, the through holes may be omitted.

Furthermore, in the above-described embodiment, although the motor caseis formed from (comprises) the upper case and the lower case, theupper-lower arrangement is a positional relationship strictly for thesake of convenience, and there is no problem with respect to theelectric work machine even if two half cases are arranged in theleft-right direction, the forward-rearward direction, a diagonaldirection, or the like.

Furthermore, any one of the cover members alone, such as the upper case,may be fixed to the housing side. In such an embodiment, because theother cover member can be omitted, ease of assembly is improved.

In addition, fins for heat dissipation may be provided on the statorcore. Moreover, the heat-dissipating properties can also be improved byconnecting structures to the motor case that have high heat-transfer(heat conductivity) properties.

Advantages of the Representative Three-Phase Coil Connection Method

In the lawn mower 1 of the above-mentioned embodiment, because the threephases of the coils 45 of the brushless motor 21 are delta connected,with each phase having four coils in parallel, the wire diameter of thewires 115A-115C can be made narrower than in a star connection, evengiven the same output, and thereby winding characteristics duringmanufacture can be improved. In addition, because the winding nozzlescan be narrowed, dead space can be reduced, which ultimately leads to anincrease in output power.

Here in particular, because the delta connection is formed by shortcircuiting, using the plurality of sheet-metal members (the first tothird metal fittings 97U-97V) mounted on the upper insulator 42, thecrossover wires 117A-C between the coils 45 wound on the teeth 41adjacent in the circumferential direction of the stator core 40 throughthe upper insulator 42, a wiring connection becomes possible in whichcomplex crossover wires, cross wires, and the like are not created.Thereby, productivity becomes high and, moreover, the risk of scrapingof the wires 115 caused by contacting each other can be reduced.

In addition, there are twelve of the coils 45 for the three phases, eachof the three wires 115 is used to continuously form four coils 45adjacent in the circumferential direction of the stator core 40.Furthermore, a start end 116A, B of one wire 115 and a terminal end118A, B, C of another wire 115 adjacent in the circumferential directionare electrically connected to each of the first to third metal fittings97U-97V with the same orientation relative to the short-circuitingmember 46. Therefore, the start ends 116A-C and the terminal ends 118 ofthe wires 115 can be cut simultaneously, whereby productivity is furtherimproved.

It is noted that in the three-phase, coil-connection method, thewire-winding method is not limited to the above-described embodiment,and there is no problem even if the coils are formed with one, two,four, or six wires using one, two, four, or six winding nozzles. Ifthere is one winding nozzle, then all twelve teeth are wound with onewire (12×1); if there are two winding nozzles, then six teeth are woundwith two wires (6×2). In addition, if there are four winding nozzles,then three teeth are wound with four wires (3×4); and if there are sixwinding nozzles, then two teeth are wound with six wires (2×6).

If there is one winding nozzle, then it takes time to wind the wire onthe teeth; however, because the number of the winding nozzles is small,the equipment is compact and equipment expenses can also be kept low. Asthe number of the winding nozzles increases, the time needed to wind thewires on the teeth decreases; however, the equipment increases in sizeand equipment expenses also increase.

In the above-mentioned embodiment, three of the winding nozzles are usedbecause that it provides an advantageous balance between time andequipment for winding the wires. However, if more importance is attachedto the advantages of equipment, then one or two of the winding nozzlesshould be used. On the other hand, if more importance is attached toreducing time requirements, then four or six of the winding nozzlesshould be used.

In addition, each phase is not limited four in parallel; five or more inparallel may be used.

Furthermore, the shape of the sheet-metal members is also not limited tothe first to third metal fittings of the above-mentioned embodiment. Forexample, the width may be increased, some of the first to third metalfittings may be made to overlap in the axial direction withoutcontacting, without being disposed concentrically, or the like.

Advantages of the Representative Diamond Knurl of the Rotary Shaft

In the lawn mower 1 of the above-mentioned embodiment, the slip torque(grip) between the rotary shaft 25 and the rotor core 55 can beincreased by the provision of the diamond knurl 25 a, which constitutesthe rotation-impeding part in the rotational direction relative to theresin 56 and the slippage-impeding part in the axial direction relativeto the resin 56, on the outer circumference of the rotary shaft 25.

Here in particular, by using the diamond knurl 25 a, slip torque (grip)in the rotational direction and slip torque (grip) in the axialdirection can be improved at the same time.

It is noted that the rotation-impeding part and the slippage-impedingpart are not limited to a shape that acts upon both, as in the diamondknurl, and it is also possible to provide only one of therotation-impeding part and the slippage-impeding part.

For example, as the rotation-impeding part, a straight knurl 25 b asshown in FIG. 19A may be provided.

In addition, the grip (unevenness) on the rotary shaft 25 is not limitedto knurling, and it is also possible to impede rotation by making thetransverse-cross-sectional shape of the rotary shaft 25 into a shapeother than a circular shape. FIGS. 19B and C show, as differently shapedparts, examples in which a bevel part 25 c extending in the axialdirection is formed at one or two locations, and FIG. 19D shows anexample in which a V-shaped groove 25 d extending in the axial directionis formed. However, the number of bevel parts may be formed at three ormore locations, and the number of the grooves also may be increased. Thegroove may have a shape other than a V shape.

Furthermore, the differently shaped part is not limited to the bevelpart, the groove, or the like, and the transverse-cross-sectional shapemay be a quadrilateral shape, a polygonal shape, or the like and may bean elliptical shape, an oval shape, or the like.

On the other hand, as the slippage-impeding part, as shown in FIG. 19E,ring grooves 25 e extending in the circumferential direction of therotary shaft 25 can also be formed at prescribed spacings in the axialdirection. There may be one or three or more of the ring grooves.Moreover, the grooves may be provided only partially in thecircumferential direction, i.e. in a ring (annular) shape.

Furthermore, the rotation-impeding part and the slippage-impeding partcan also be combined. For example, if the ring groove is combined withthe straight knurl or if the ring groove is combined with a differentlyshaped part configured as a bevel part, a groove, or the like, then theeffect of both rotation impeding and slippage impeding are obtained.

Advantages of the Representative Insulating Means Between the StatorCore and the Rotary Shaft

The lawn mower 1 of the above-described embodiment comprises: themain-body housing 10 (an exterior housing); the motor case 22 (aninterior case) fixed inside the main-body housing 10; the brushlessmotor 21 housed inside the motor case 22 and comprising the stator 23having the stator core 40, the coils 45, and the upper and lowerinsulators 42, 43, and the rotor 24 disposed inward of the stator 23 andhaving the rotary shaft 25; and the spindle 17 (an output part) drivenby the rotary shaft 25. The motor case 22 holds the stator 23 andaxially supports the rotary shaft 25 via bearings 68, 76. The insulatingcap 67 and the resin layer 78 (which are each an insulating means)provide electrical insulation between the stator core 40 and the rotaryshaft 25. Therefore, even if the brushless motor 21 is housed in the(metal) motor case 22 inside the main-body housing 10, double insulationbecomes possible in which the conducting pathway from the (metal) statorcore 40 through the (metal) motor case 22 to the (metal) rotary shaft 25can be effectively insulated.

Here in particular, because the resin 56 (the insulating member on therotary-shaft side) is interposed between the rotor core 55 and therotary shaft 25, which are provided in the rotor 24, more effectiveinsulation becomes possible.

In addition, because the insulating means may include the insulating cap67 (bearing-side insulating member), which is provided at a portion ofthe motor case 22 that rotatably supports the rotary shaft 25 via thebearing 68, and/or the resin layer 78 (stator-side insulating member),which is provided between the motor case 22 and the stator core 40, theinsulating means can be formed effectively.

Furthermore, if the resin layer 78 is integrally formed on (joined to)the lower case 27 of the motor case 22, it becomes possible to form theresin layer 78 in a simple manner at the time of manufacturing the lowercase 27.

It is noted that the insulating means according to the present teachingsis not limited to the insulating cap 67 and the resin layer 78 of theabove-described embodiment. For example, as the bearing-side insulatingmember, a resin material (electrically insulating resin or polymermaterial) may be interposed between the bearing and the rotary shaft. Inaddition or in the alternative, as the stator-side insulating member, anelectrically insulating resin or polymer layer may be formed on theouter side of the rotor core. The bearing-side insulating member canalso be integrally formed with (on) the motor case. In addition or inthe alternative, either one or both of the upper case and the lower caseof the motor case can also be made of resin or polymer. Furthermore, thebearing-side insulating member and/or the stator-side insulating membercan also be used in combination. Either one of the bearing-sideinsulating member and the stator-side insulating member can also beomitted.

In another embodiment of the present teachings, a compressor 120 isschematically shown in FIG. 20. In the compressor 120, the stator 23 ofthe brushless motor 21 is supported on the outer side of a housing 121via a stator-support member 122, which has a bottomed-tube shape.Furthermore, the rotary shaft 25 extends into the housing 121 and isconnected to an output part (not shown), which may be e.g., a piston,rotary screw, vane, scroll, etc. In addition, a first insulating member123 is interposed between the stator-support member 122 and the statorcore 40 and a second insulating member 124 is interposed between therotary shaft 25 and the rotor core 55, thereby providing doubleinsulation between the stator core 40 and the rotary shaft 25 on oneside and the housing 121 on the other (here, although not shown, basicinsulation is also implemented by interposing a basic-insulation memberbetween the coils and the stator core, as in the above-describedembodiment).

It is noted that the housing 121 and the stator-support member 122herein may be integral. In addition or in the alternative, therotation-impeding part and/or the slippage-impeding part, such as adiamond knurl, also may be fabricated on the rotary shaft 25.

Finally, it should be noted the present teachings are applicable toother types of electric work machines, i.e. other than a lawn mower, acompressor, or the like. For example, the present teachings may besuitably applied to gardening tools (e.g., outdoor power equipment),such as electrically powered chain saws, hedge trimmers, mowingmachines, blowers, and the like, as well as to other types of powertools, such as angle drills, grinders, hammers, hammer drills, circularsaws, reciprocating saws (“recipro saws”), and the like. Thus, in suchembodiments, the output part of the electric work machine may be e.g., asaw chain, shears, a blower fan, a tool chuck, a tool holder, a disk(e.g., a grinding, sanding or polishing disk), a cutting blade, apiston, etc.

Representative, non-limiting examples of the present invention weredescribed above in detail with reference to the attached drawings. Thisdetailed description is merely intended to teach a person of skill inthe art further details for practicing preferred aspects of the presentteachings and is not intended to limit the scope of the invention.Furthermore, each of the additional features and teachings disclosedabove may be utilized separately or in conjunction with other featuresand teachings to provide improved brushless motors and electric workmachines that utilize such brushless motors.

Moreover, combinations of features and steps disclosed in the abovedetailed description may not be necessary to practice the invention inthe broadest sense, and are instead taught merely to particularlydescribe representative examples of the invention. Furthermore, variousfeatures of the above-described representative examples, as well as thevarious independent and dependent claims below, may be combined in waysthat are not specifically and explicitly enumerated in order to provideadditional useful embodiments of the present teachings.

All features disclosed in the description and/or the claims are intendedto be disclosed separately and independently from each other for thepurpose of original written disclosure, as well as for the purpose ofrestricting the claimed subject matter, independent of the compositionsof the features in the embodiments and/or the claims. In addition, allvalue ranges or indications of groups of entities are intended todisclose every possible intermediate value or intermediate entity forthe purpose of original written disclosure, as well as for the purposeof restricting the claimed subject matter.

EXPLANATION OF THE REFERENCE NUMBERS

-   -   1 Lawn mower    -   2 Base    -   3 Main body    -   4 Handle    -   10 Main-body housing    -   15 Controller    -   16 Motor unit    -   17 Spindle    -   20 Cutting blade    -   21 Brushless motor    -   22 Motor case    -   23 Stator    -   24 Rotor    -   25 Rotary shaft    -   25 a Diamond knurl    -   26 Upper case    -   27 Lower case    -   40 Stator core    -   40 a Steel plate    -   41 Tooth    -   42 Upper insulator    -   43 Lower insulator    -   45 Coil    -   46 Short-circuiting member    -   47 Sensor circuit board    -   48A, 48B Ridge    -   50A, 50B Projection    -   54 Split mold    -   55 Rotor core    -   56 Resin (representative insulating member)    -   65 Fin    -   67 Insulating cap (representative insulating means)    -   71A, 71B Screw-boss part    -   78 Resin layer (representative insulating means)    -   79A, 79B Boss part    -   81 Screw    -   85 Terminal-holding part    -   97U-97V First to third metal fittings    -   99 Fusing terminal    -   115 Wire    -   120 Compressor    -   122 Stator-support member    -   123, 124 Insulating member

We claim:
 1. An electric work machine comprising: an exterior housing;an interior case fixed inside the exterior housing; a brushless motorhoused inside the interior case, the brushless motor comprising astator, which has a stator core, one or more coils, and an insulatorinterposed between the stator core and the coil(s), and a rotor disposedinward of the stator and having a rotary shaft; and an output partdriven by the rotary shaft; wherein: the interior case holds the statorand axially supports the rotary shaft via a bearing; and an electricallyinsulating means is provided between the stator core and the rotaryshaft.
 2. The electric work machine according to claim 1, furthercomprising an electrically insulating member interposed between a rotorcore of the rotor and the rotary shaft.
 3. The electric work machineaccording to claim 2, wherein: the electrically insulating member is aninsert made of electrically insulating resin or polymer; and the rotaryshaft has an uneven surface that impedes rotation of the insert relativeto the rotary shaft and/or impedes slippage of the insert relative tothe rotary shaft in an axial direction of the rotary shaft.
 4. Theelectric work machine according to claim 1, wherein the electricallyinsulating means includes a bearing-side insulating member provided inor on a portion of the interior case that axially supports the rotaryshaft via the bearing.
 5. The electric work machine according to claim4, wherein the bearing-side insulating member is formed separately fromthe interior case and is integrally attached to the interior case. 6.The electric work machine according to claim 4, wherein: thebearing-side insulating member is a cap made of electrically insulatingresin or polymer; and the cap is fitted between the bearing and abearing retaining part defined in the interior case.
 7. The electricwork machine according to claim 6, wherein the cap is integrally formedon the interior case.
 8. The electric work machine according to claim 4,wherein the bearing-side insulating member is integrally formed on theinterior case.
 9. The electric work machine according to claim 1,wherein the electrically insulating means includes a stator-sideinsulating member interposed between the interior case and the statorcore.
 10. The electric work machine according to claim 9, wherein thestator-side insulating member is integrally formed on the interior case.11. The electric work machine according to claim 10, wherein thestator-side insulating member is a layer made of electrically insulatingresin or polymer attached to an inner surface of the interior case. 12.The electric work machine according to claim 1, wherein the interiorcase, the stator core and the rotary shaft are each made of a metal. 13.The electric work machine according to claim 12, wherein theelectrically insulating means includes: a cap made of electricallyinsulating resin or polymer, the cap being fitted between the bearingand a bearing retaining part defined in the interior case; and a layermade of electrically insulating resin or polymer attached to an innersurface of the interior case so as to be interposed between the interiorcase and the stator core; wherein: an insert made of electricallyinsulating resin or polymer is interposed between a rotor core of therotor and the rotary shaft; and the rotary shaft has an uneven surfacethat impedes rotation of the insert relative to the rotary shaft and/orimpedes slippage of the insert relative to the rotary shaft in an axialdirection of the rotary shaft.
 14. An electric work machine comprising:a brushless motor comprising a stator, which has a stator core, one ormore coils, and an insulator interposed between the stator core and thecoil, and a rotor disposed inward of the stator and having a rotaryshaft; an output part driven by the rotary shaft; a stator-supportmember that supports the stator; a housing that supports thestator-support member; and an electrically insulating means providingelectrical insulation between the stator core and the rotary shaft. 15.The electric work machine according to claim 14, further comprising aninsulating member interposed between the housing and the stator core.16. The electric work machine according to claim 14, wherein theinsulating member is a layer made of electrically insulating resin orpolymer.
 17. A brushless motor comprising: a stator having a statorcore, coils wound on the stator core, and an insulator interposedbetween the stator core and the coils; and a rotor disposed in theinterior of the stator and having a rotary shaft, wherein: the statorcore is composed of a plurality of steel plates stacked in an axialdirection of the brushless motor; on an outer circumference of thestator core and/or of the steel plates, a plurality of recesses and/orridges having through holes and/or projections having through holes areformed; and a plurality of screws or bolts respectively engage in therecesses and/or extend through the through holes of the ridges and/or ofthe projections.
 18. The brushless motor according to claim 17, furthercomprising: a motor case having a first half case and a second halfcase; wherein: screw boss parts are formed on an outer circumference ofthe first half case and respectively receive a first end of the ridges;and boss parts are formed on an outer circumference of the second halfcase and respectively receive a second end of the ridges.
 19. Thebrushless motor according to claim 18, wherein: the first half case ismade of metal; the first half case has a bearing retaining part thatholds a bearing via an electrically-insulating cap that is interposedbetween a metallic portion of the first half case and the bearing; andthe bearing rotatably supports one end portion of the rotary shaft. 20.The brushless motor according to claim 18, wherein: the second half caseis made of metal; and an electrically-insulating resin or polymer layeris disposed at least on an inner surface of the second half case suchthat the electrically-insulating resin or polymer layer is interposedbetween the stator core and a metallic portion of the second half case.21. The brushless motor according to claim 18, wherein one of theridges, one of the projections, one of the screw boss parts and/or oneof the boss parts has/have a different outer contour than the otherridge(s), projection(s), screw boss part(s) and boss part(s).
 22. Thebrushless motor according to claim 21, wherein: the first half case andthe second half case are each made of metal; the first half case has abearing retaining part that holds a bearing via anelectrically-insulating cap that is interposed between a metallicportion of the first half case and the bearing; the bearing rotatablysupports one end portion of the rotary shaft; and anelectrically-insulating resin or polymer layer is disposed at least onan inner surface of the second half case such that theelectrically-insulating resin or polymer layer is interposed between thestator core and a metallic portion of the second half case.